1. Field of the Invention
The invention relates to motor operators, such as for power switches of electrical utilities, and particularly to such operators for underground switches as well as switches in other locations, with a drive and control system that allows remote adjustment of motor travel settings and other features facilitating their construction and operation.
2. Background Art
Power switches, for example, disconnect and load break switches for distribution systems, are typically used in three main types of locations: overhead on a utility pole, in an underground vault, and pad mounted substantially at surface level. (Reference to “pad” or “pad mounted” herein, unless the context clearly indicates the contrary, is to be understood as mounted on an above ground pad. It is of course the case that underground switches are sometimes mounted on a pad also.) The switches can also be of different types. Unenclosed air break switches are often used on pole top installations. Enclosed, but not sealed, air break switches are often used at pad mounted installations. Enclosed and sealed switches, such as with vacuum or gas (e.g., SF6) insulation, are often used in locations, such as underground vaults, where the confined and sometimes flooded space makes them preferred to air break switches.
Switches in underground locations, and also in some pad installations, have motor operators located near the switches (in contrast, for example, to poletop air break switches that are mechanically coupled to motor operators on or near the ground). At one time power switches could be operated only by direct access to the switch or its operator. More recently, the power switch art has applied technology for remote, automated, operation of a motor operator to close and open a power switch, (see, for example, Cleaveland/Price Bulletin DB-128C01 (of 2001), and also, U.S. Pat. No. 6,075,688, Jun. 13, 2000, herein incorporated by reference, for background information on automated motor operators). Sometimes, however, a motor operator will need some adjustment performed at the motor operator itself.
Extra danger to utility workers is encountered in tight locations such as underground vaults. For example, an enclosed switch may explode, due to heat buildup from arcing, and subject workers to injury.
Motor operators for underground switch locations generally require a sealed enclosure. For access to the interior of the enclosure, it has been necessary to have a port or panel of the enclosure that is removable and replaceable at the service location by a worker. In addition to the time needed to access the interior and to reseal the motor operator properly, perhaps dealing with up to thirty fasteners and a gasket, there is a risk the attempt to reseal is not successful and can lead to malfunction of the unit. The worker performing the field work is not equipped to test whether the seal is effective.
In the past, underground motor operators, and most others, required adjustment at the motor operator-power switch location to set the limits of travel of the motor in the motor operator which determine the travel limits of the power switch. For proper operation the motor drive unit (i.e., the motor itself and related gearing) needs to be able to move the power switch contacts to a definite closed position or a definite open position. Otherwise the function of the switch is impaired and, possibly, the motor of the drive or the mechanical coupling to the switch is damaged by being driven until the motor stalls.
For final adjustment during installation and occasional readjustment over the life of the equipment, in the case of an underground switch, a worker would have to enter the vault where the switch and motor operator are located. Typically, limit switches to control the limits of travel of the motor operating shaft would need setting upon initial installation of the operator and switch and possible adjusting from time to time after installation. The limit switches would have to be accessed by opening up the enclosure containing the motor resulting in the risks mentioned above in the case of underground units, including at least the risk to the integrity of the seal of the enclosure. While other locations, such as pad mounted at ground level, do not involve quite the same concerns for worker safety and motor operator integrity, the need for accessing limit switches is at least an undesirable maintenance requirement.
Motor operators have been used or proposed having a switch actuator with a position-sensing feature between an output shaft of the motor of the operator and a lever that produces power switch opening or closing, for example, as in U.S. Pat. No. 5,552,647, Sep. 3, 1996. Position sensing is shown by a potentiometer responsive to movement of a linear actuator to generate a signal indicating a position of a reference element on the actuator. The signal generated is communicated to control circuitry. The circuitry compares the signal to a standard to determine if the actuator travel is within limits determined by adjustable open-limit and closed-limit potentiometers. The arrangement is intended to improve on prior limit switch assemblies which fail to provide sufficient accuracy and repeatability and tend to be overly complicated and costly.
Such an actuator control is not one that avoids need for adjustment in the motor operator enclosure. The enclosure has an access hole specifically for adjustment of the open-limit potentiometer and the close-limit potentiometer.
Other motor operators have been disclosed that also have a sensed position signal. U.S. Pat. No. 6,025,657, Feb. 15, 2000, is directed to a motor operator for either power or manual operation without need for any decoupling or mode selection with a control system that receives signals indicating both the position of the drive output and the current drawn by the drive source. U.S. Pat. No. 6,215,263, Apr. 10, 2001, discloses a motor operator for overhead air break switches with a microcontroller subject to a variety of signals, including a position signal developed by a sensor that is a type of encoder. Some of the parameters relied on are temperature sensitive and require compensation. Some types of shaft position sensors, for example, including some encoders, depend on continuous power for a position signal to be reliably generated. Otherwise, after a power outage, the actual switch position would need to be observed and the motor travel limits reset. Such prior art has not particularly addressed and responded to a desire in the power switch art for avoiding needed travel limit adjustments in the enclosure of the motor, particularly important in underground sealed units, in a system not requiring multiple sensed signals and, also, easy to implement and operate.
Switches on motor operators are subject to manual operation under various circumstances. The power normally is off for a manual operation of the switch. Unless the motor is decoupled from the switch and only the switch is operated during a manual operation, there is a risk that the motor is caused to rotate at such high speed, i.e., an overspeed, that the motor is damaged (particularly its windings). Normally that risk is avoided by selecting a motor in the original manufacture that is heavy and strong enough, which of course incurs size and cost drawbacks. Similarly, any other component running off the motor shaft has to be rugged enough to withstand force that is transmitted by the shaft rotation during any operation.